The plaintiffs played during a period of time where the NFL players were not working under a collective bargaining agreement.

The lawsuit claims that the team "marginalized the risks of brain injuries and regularly referred to concussions as 'getting your bell rung' or a 'ding.'" Attorneys said players were routinely sent back into games a short time later and told there was little risk to it.

"I would have liked to have the opportunity to know that going back on the field would cause me to have severe disabilities later in life," Martin said. "I didn't know that. That's what the lawsuit is about."

Concussion awareness has evolved dramatically over the past decade, especially in the past few years. Doctors who used to think that CTE could only be diagnosed after a patient's death now think it may be possible to do so sooner. Sports leagues now have protocols in place to deal with head injuries.

"I can tell you in the last two years, the knowledge base in regards to concussion management, diagnosis, awareness and treatment is exponential in what we've learned," said Dr. Michael Moncure of the Center for Concussions at the University of Kansas Hospital. "So there is not even a comparison from what we know now from two years ago."

The lawsuit is the first filed against a specific NFL team. Plaintiffs attorney Ken McClain said Missouri's worker's compensation laws presented an opportunity for the lawsuit because of a 2005 amendment regarding long-term occupational injuries.

A class-action lawsuit against the National Football League as a whole reached a $765 million settlement earlier this year. The attorneys in the new case said the plaintiffs would only receive medical monitoring and not financial compensation from the previous settlement.

McClain said the settlement is small change for a big problem.

"It's not very much money," he said. "For the Chiefs, it's $1.2 million a year, so it's not a very adequate settlement for our view, for these players who have substantial injuries in the case, but more importantly, our players are not covered for the bulk of the money."

If more players like the five plaintiffs opt out of the settlement, that deal could fall apart.

The Kansas City Chiefs and NFL spokesman Greg Aiello declined to comment on the lawsuit.